GroupEnumerator.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading.Tasks;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Model;
using Waher.Script.Persistence.SQL.Enumerators;
 
namespace Waher.Script.Persistence.SQL.Groups
{
    public class GroupEnumerator : IResultSetEnumerator
    {
        private readonly ScriptNode[] groupBy;
        private readonly ScriptNode[] groupNames;
        private readonly Variables variables;
        private readonly IResultSetEnumerator e;
        private bool processLast = false;
        private GroupObject current = null;
        private ObjectProperties objectVariables = null;
 
        public GroupEnumerator(IResultSetEnumerator ItemEnumerator, Variables Variables, ScriptNode[] GroupBy, ScriptNode[] GroupNames)
        {
            this.e = ItemEnumerator;
            this.variables = Variables;
            this.groupBy = GroupBy;
            this.groupNames = GroupNames;
        }
 
        public object Current => this.current;
 
        public bool MoveNext()
        {
            return this.MoveNextAsync().Result;
        }
 
        public async Task<bool> MoveNextAsync()
        {
            List<object> Objects = null;
            IElement E;
            object[] Last = null;
            int i, c = this.groupBy.Length;
            object o1, o2;
 
            while (this.processLast || await this.e.MoveNextAsync())
            {
                this.processLast = false;
 
                if (this.objectVariables is null)
                    this.objectVariables = new ObjectProperties(this.e.Current, this.variables);
                else
                    this.objectVariables.Object = this.e.Current;
 
                if (Last is null)
                {
                    Last = new object[c];
 
                    for (i = 0; i < c; i++)
                    {
                        E = this.groupBy[i].Evaluate(this.objectVariables);
                        Last[i] = E.AssociatedObjectValue;
                    }
                }
                else
                {
                    for (i = 0; i < c; i++)
                    {
                        E = this.groupBy[i].Evaluate(this.objectVariables);
 
                        o1 = Last[i];
                        o2 = E.AssociatedObjectValue;
 
                        if (o1 is null ^ o2 is null)
                            break;
 
                        if (!(o1 is null) && !o1.Equals(o2))
                            break;
                    }
 
                    if (i < c)
                    {
                        this.processLast = true;
                        break;
                    }
                }
 
                if (Objects is null)
                    Objects = new List<object>();
 
                Objects.Add(this.e.Current);
            }
 
            if (Objects is null)
                return false;
 
            this.current = new GroupObject(Objects.ToArray(), Last, this.groupNames, this.variables);
 
            return true;
        }
 
        public void Reset()
        {
            this.e.Reset();
            this.processLast = false;
            this.current = null;
        }
    }
}